JPS58105430A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium having excellent dispersibility, surface smoothness and durability by contg. a specific polyurethane resin and a vinyl chloride-vinyl acetate copolymer as binder components and crosslinking the same with an isocyanate compd. CONSTITUTION:A vinyl chloride-vinyl acetate copolymer contg. >=15% maleic acid is combined with a polyurethane resin contg. -SO3 (M: metal) and further both are crosslinked with an isocyanate compd. The isocyanate compd. is isocyanate compds. contg. >=2 isocyanate groups or their adducts (adducts such as dimers, trimers, etc. or adducts, etc. with polyhydric alcohol of bivalency or trivalency). The magnetic powder is gamma-iron oxide, cobalt-deposited gamma-iron oxide, cobalt doped gamma-iron oxide, CrO2, alloy magnetic powder, metallic magnetic powder, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium that has excellent dispersibility of magnetic particles in a magnetic coating, excellent smoothness of the coated surface, and excellent durability.

Magnetic recording tape, especially video recording tape, has a magnetic particle of 11111! Uniform dispersibility in I and a high degree of surface smoothness of the magnetic coating are required, and physical properties such as reliability and durability that can withstand use over a longer period of time and in a greater number of times are required. .

In order to meet the above requirements, conventional combinations of various resins have been developed as binders for magnetic IIi! It's been pointed out. Although these proposals have produced some results in terms of physical properties, it cannot be said that improvements in dispersibility and surface smoothness are still in a satisfactory state.

Techniques that have been proposed to improve dispersibility include, for example, the use of surfactants as dispersants, or the use of hydrophilic groups (such as [OH groups, coon groups) in the binder resin molecules.
There are methods such as increasing the content of M, but the former has problems such as deterioration of physical properties and changes over time due to the presence of low molecular weight surfactants in the magnetic m film, and the latter has some problems such as deterioration of physical properties and changes over time. Although an improvement was seen, sufficient dispersion could not be obtained in cases where dispersible ab-like substances such as car y platters were included, or when used in combination with resins with poor dispersibility. In addition, generally speaking, if the dispersibility improves, the surface smoothness will also improve, but even if IIt fat with poor dispersibility is used, if a large amount of soft*shield is used, it will not be possible to perform a calendar surface treatment. Although modulation noise due to surface smoothness can be lowered than K, there is noise due to insufficient dispersion.

Moreover, by using a lot of soft IM) fr, the stiffness of the magnetic coating film increases, which is not desirable in terms of durability and the like.

The object of the present invention is to improve these drawbacks and provide a magnetic recording medium that has excellent dispersibility, surface smoothness, and durability.

As a result of various studies and dormitory experiences, the inventors of the present invention have developed a binder component that uses a special polyurethane resin with extremely high dispersibility and a vinyl chloride-vinyl acetate copolymer with improved dispersibility. By crosslinking this with an incyanate compound, it was possible to provide a recording medium with excellent dispersibility, surface smoothness, and durability.

The polyurethane resin used in the present invention is a group consisting of -UK metal sulfonate, preferably a sulfoboricreathane resin. By having one -80 group as one chain, a binder can be provided which exhibits the same effect as using a dispersant and does not have the disadvantages of using a low molecular weight dispersant.

The present inventor proposed a magnetic recording medium using a polyurethane resin containing sodium sulfonate groups in Japanese Patent Application No. 55-152545.

This dramatically improved the dispersibility of the polyurethane resin cape, but when used in combination with other resins to improve the #II physical properties of magnetic recording media, there was a tendency for the dispersibility to be somewhat inhibited. .

Therefore, as a result of intensive search for a binder composition free from the above-mentioned drawbacks, the present invention combines the above-mentioned improved polyurethane resin with a vinyl chloride/vinyl acetate copolymer containing more than a t-ts of maleic acid, and further incorporates these. By crosslinking with a cyanate compound, a magnetic recording medium with extremely improved dispersibility and surface smoothness and excellent running durability could be obtained.

-80. which can be used in the present invention. Na group-containing polyurethane*
* indicates dicarboxylic acid components (terephthalic acid, isophthalic acid, sebacic acid, etc.), polyhydric alcohol components (ethylene glycol, neopentyl/IJ*-ru, etc.), and -
Polyester IIM& obtained by polycondensing a dicarboxylic acid component (5-sodium sulfoisophthale Il*) having 80,N1 groups is urethanized with diphenylmethane 446 diincyanate (MDI), but it is necessary to
According to NK [Combination of various dicarboxylic acids and polyhydric alcohol components as ingredients to produce polyester resin]
Various diisocyanate compounds, such as hexamethylene diisocyanate, can be used as the incyanate component to be reacted with the polyester.
) (HMDI), toluene diisocyanate (TDI)
, L5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine diisocyanate methyl ester (LDI), etc. can be used.

In Japanese Patent Application No. 54-157728, the present inventor proposed an all-in-one recording medium in which a vinyl chloride-vinyl acetate copolymer containing a vinyl alcohol component of SS or more is used in combination with a polyurethane resin containing a sulfone metal base. As a result, the dispersibility of the binder was dramatically improved, and a magnetic recording medium with extremely excellent surface slipperiness was obtained, but because it contained vinyl alcohol, its glass transition point
The temperature was as high as 75°C, which tended to somewhat inhibit the improvement of surface properties by calendering.

Therefore, the inventor of the present invention aimed to create a recording medium using a vinyl chloride-vinyl acetate copolymer that has good dispersibility and has a higher glass transition point than the vinyl chloride-vinyl acetate copolymer. We conducted extensive research on how to incorporate functional groups. As a result, when maleic acid was contained in the vinyl chloride-vinyl acetate copolymer at ts1 or more, the dispersibility was good, the glass transition temperature hardly changed (65-66°C), and the calendering processability was excellent. It was discovered that a resin can be obtained, and the present invention was particularly completed.

That is, the vinyl chloride/vinyl acetate copolymer containing maleic acid fkts or more has extremely excellent dispersibility as a vinyl chloride/vinyl acetate copolymer.

By using the present invention in combination with a resin that has processability and excellent dispersibility as in the present invention, it is possible to provide a binder for magnetic recording media with extremely high dispersibility, which has not been previously available.

The combination of urethane resin and vinyl chloride/vinyl acetate copolymer has excellent running durability as a binder for magnetic recording media. 50° C.), it was found that it could not be said to have sufficient durability. The present invention also improves this point by performing crosslinking using an incyanate compound, and provides a magnetic recording medium with excellent dispersibility, surface smoothness, and durability. It is. The incyanate compound that can be used in the present invention is an isocyanate compound having two or more isocyanate groups, or an adduct thereof such as a 21-mer or a pentamer, or a divalent compound.

The magnetic powder used in the present invention includes r-iron oxide, cobalt-coated r-iron oxide, balt-doped r-iron oxide, Cr
O2, alloy magnetic powder, metal magnetic powder.

Further, an antistatic agent, carbon black, lubricant, and non-magnetic inorganic pigment may be added as necessary.

The present invention will be explained in detail below.

The resins used in the examples of the present invention are shown below.

Polyurethane resin Vinyl chloride/vinyl acid copolymer Injection: A copolymer of vinyl chloride 97-1 and vinyl 97-1, copolymerized with maleic acid.

Example Table 1 Trial 15 As the salt-vinyl acetate, a salt-vinyl acetate copolymer containing 80% vinyl alcohol was used in combination with a polyurethane material containing 180sNa, and a cobalt-coated r-Fe20. 400 Polyurethane II fat (according to Table 1) 50 Vinyl chloride/vinyl acetate copolymer (according to Table 1) 50 Carbon black 30 Lubricant
10 Non-magnetic application fee
20 Methyl ethyl ketone 400 Toluene 400 After thoroughly dispersing the above composition using the resin combination shown in Table 1 by a commonly used method, it was spread on a polyethylene terephthalate film with a K11k cloth so that the film had a thickness of 5μ after drying, was dried, and calendered. .

When the surface reflectance of the magnetic coating film of the obtained magnetic recording medium was measured, the results shown in the figure were obtained. 1 to 13 in the figure are sample 1
Corresponds to ~15.

As can be seen from the above results, -80
When the sNa group is included, the surface smoothness of the recording medium is greatly improved compared to K. Furthermore, when the content of maleic acid in the vinyl chloride/vinyl acetate copolymer is increased, the surface smoothness is further improved, and when it exceeds about tsl, the effect on the surface smoothness is saturated. In addition, processability is improved compared to those containing vinyl arsul.

After adding 20 parts by weight of Desmodinyl L (manufactured by Bayer) as an incyanate compound to the coating composition of Sample 12, which is one of the best among Samples 1 to 12, the same treatment process as Samples 1 to 12 was applied. Apply by the method of
After drying and calendering, the tape was cured by heating at a predetermined temperature and cut into appropriate widths to obtain a magnetic recording tape (hereinafter referred to as Example tape). On the other hand, sample 1
A similar tape version of the magnetic recording medium of No. 2 (hereinafter referred to as a comparison tape) was used for comparison.

The results are shown in the table below.

From the above results, a magnetic recording medium using a polyurethane resin containing 180 sNa and a vinyl chloride/vinyl acetate copolymer containing 15 or more maleic acid as a binder component and an incyanate compound as a crosslinking agent has a good dispersibility and surface It has excellent properties and durability.

The desired effects of the present invention can also be obtained by using a polyurethane/11 resin containing general K-80,M (M: metal).

[Brief explanation of the drawing]

The drawing is a graph showing the influence of the maleic acid component in the vinyl chloride/vinyl acid copolymer and the sodium sulfonate group in the polyurethane resin on the surface reflectance of a magnetic recording medium.

Claims (1)

[Scope of Claims] t) A binder consisting of a polyurethane resin having a sulfonic acid metal salt group and a vinyl chloride/vinyl acetate copolymer containing 1,596 or more maleic acids contains an incyanate compound as a crosslinking agent to create magnetic properties. A magnetic recording medium consisting of a magnetic coating coated with powder dispersed on a support. 2 The group of the sulfonic acid metal salt is -80sNa, claims! The magnetic recording medium according to item 1.